Final drive mechanism for a transmission

ABSTRACT

A final drive mechanism includes a pinion, a gear meshing with the pinion, a differential mechanism, and a first gearset including an input driveably connected to the gear, and an output driveably connected to the differential, rotating slower than a speed of the gear, and rotating in a direction opposite the direction of the gear.

This application claims priority to and the benefit of U.S. ProvisionalApplication No. 61/446,154, filed Feb. 24, 2011, the full disclosure ofwhich is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an automatic transmission for a motor vehiclethat includes planetary gearsets and clutches and brakes whose state ofengagement and disengagement determines speed ratios produced by thetransmission.

2. Description of the Prior Art

In a front wheel drive vehicle, the axial space available for thetransmission is limited by the width of the engine compartment and thelength of the engine. In addition, the trend to increase the number ofratios available generally increases the number of components required.For these reasons, it is desirable to position components concentricallyin order to minimize axial length. The ability to position componentsconcentrically is limited, however, by the need to connect particularcomponents mutually and to the transmission case.

Furthermore, it is desirable for the output element to be located nearthe center of the vehicle, which corresponds to the input end of thegear box. An output element located toward the outside of the vehiclemay require additional support structure and add length on the transferaxis. With some kinematic arrangements, however, the need to connectcertain elements to the transmission case requires that the outputelement be so located.

Chain drive transaxle final drive systems with grounded ring planetarygear sets have unacceptable noise, vibration and harshness propertiesdue to chain lash. Transfer shaft gearing systems limit overall gearratio.

SUMMARY OF THE INVENTION

A final drive mechanism includes a pinion, a gear meshing with thepinion, a differential mechanism, and a first gearset including an inputdriveably connected to the gear, and an output driveably connected tothe differential, rotating slower than a speed of the gear, and rotatingin a direction opposite the direction of the gear.

The gear drive and grounded carrier planetary gearset eliminate chainlash and provide greater speed reduction potential than does a transfershaft design.

The scope of applicability of the preferred embodiment will becomeapparent from the following detailed description, claims and drawings.It should be understood, that the description and specific examples,although indicating preferred embodiments of the invention, are given byway of illustration only. Various changes and modifications to thedescribed embodiments and examples will become apparent to those skilledin the art.

DESCRIPTION OF THE DRAWINGS

The invention will be more readily understood by reference to thefollowing description, taken with the accompanying drawings, in which:

FIG. 1 is a cross sectional side view of a multiple speed automatictransaxle;

FIG. 2 is cross sectional side view of the transaxle showing the frontand middle cylinder assemblies;

FIG. 3 is a side perspective view showing sleeves that are fitted on thefront support and middle cylinder assembly, respectively;

FIG. 4 is a cross sectional side view of the transfer gears and shaftnear the output of the transaxle of FIG. 1; and

FIG. 5 is a cross sectional side view of a multiple speed automatictransaxle having an alternate final drive mechanism from that of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, FIG. 1 illustrates gearing, clutches,brakes, shafts, fluid passages, and other components of a multiple-speedautomatic transaxle 10 arranged substantially concentrically about anaxis 11.

A torque converter includes an impeller driven by an engine, a turbinehydrokinetically coupled to the impeller, and a stator between theimpeller and turbine. A transmission input shaft 20 is secured by aspline connection 21 to the turbine. The stator is secured by a splineconnection 22 to a front support 24, which is secured against rotationto a transmission case 26.

A double pinion, speed reduction planetary gearset 28 includes a sungear 30, secured by a spline connection 31 to input shaft 20; a carrier32, secured by a spline connection 33 to the front support 24; a ringgear 34, secured by a spline connection 35 to a front cylinder assembly36; a first set of planet pinions 38 supported on carrier 32 and meshingwith sun gear 30; and a second set of planet pinions 40, supported oncarrier 32 and meshing with ring gear 34 and the first pinions 38. Ringgear 34 rotates in the same direction as input shaft 20 but at a reducedspeed.

Rear gearset 46 and middle gearset 48 are simple planetary gearsets.Gearset 46 includes a set of planet pinion 50 supported for rotation oncarrier 52 and meshing with both sun gear 54 and ring gear 56. Gearset48 includes a set of planet pinions 58 supported for rotation on carrier60 and meshing with both sun gear 62 and ring gear 64. Sun gear 54 issplined to a shaft that is splined to a shell 66, on which shaft sungear 62 is formed, thereby securing the sun gears 54, 62 mutually and tothe shell 66. Carrier 52 is fixed to a shell 68. Carrier 60 and ringgear 56 are fixed to each other and to output pinion 70 through a shell72. Ring gear 64 is fixed to shell 74.

Front cylinder assembly 36, which is fixed to ring gear 34, actuatesclutches 76, 80. Plates for clutch 76 includes plates splined to frontcylinder assembly 36 alternating with plates splined to shell 74. Whenhydraulic pressure is applied to piston 78, the plates are forcedtogether and torque is transmitted between ring gears 34 and 64. Whenthe hydraulic pressure is released, ring gears 34 and 64 may rotate atdifferent speeds with low parasitic drag. Similarly, plates for clutch80 include plates splined to front cylinder assembly 36 alternating withplates splined to shell 66. When hydraulic pressure is applied to piston82, torque is transmitted between ring gear 34 and sun gears 54, 62.Pressurized fluid is routed from a control body 84, through frontsupport 24, into front cylinder assembly 36 between rotating seals.

Middle cylinder assembly 86, which includes carrier 32, actuates brake88. Plates for brake 88 include plates splined to carrier 32 alternatingwith plates splined to shell 66. When hydraulic pressure is applied topiston 90, the brake holds sun gears 54, 62 against rotation.Pressurized fluid is routed from the control body 84, through frontsupport 24, between planet pinions 38, 40, into middle cylinder assembly86. Due to the location of clutch pack 88, output element 70 is locatedin the more favorable position near the front of the gear box.

Rear cylinder assembly 92 is secured by a spline connection 93 fixed toinput shaft 20. When hydraulic pressure is applied to piston 94, theplates of clutch 96 transmit torque between input shaft 20 and carrier52. Similarly, when hydraulic pressure is applied to piston 98, theplates of clutch 100 transmit torque between input shaft 20 and sungears 54, 62. Pressurized fluid is routed from the control body 84, intorear cylinder assembly 92.

When hydraulic pressure is applied to piston 102, brake 104 holdscarrier 52 and shell 68 against rotation. A one-way brake 106 passivelyprevents carrier 52 and shell 68 from rotating in the negativedirection, but allows them to rotate in the forward direction. One-waybrake 106 may optionally be omitted and its function performed byactively controlling brake 104.

The D brake 104 is used only as a latching device not as a dynamicbrake. To minimize parasitic viscous drag loss produced in brake 104 itis desired that excess oil not be present in the brake. Therefore, anoil dam formed by an oil seal 103 between the piston 94 of E clutch 96and the inner race 107 of one-way brake 106 is provided to limit orprevent oil from entering the D brake 104. The inner radial end ofreturn spring 108 continually contacts the piston 102 that actuatesbrake 104. The outer radial end of return spring 108 continuallycontacts a fixed structure, so that the spring flexes as the piston 102moves in the cylinder of the D brake 104. In this way, return spring 108also participates in the oil dam by limiting or preventing radial flowof oil into the D brake 104 caused by centrifugal force.

This arrangement permits brake 88 and clutches 76, 80 to be mutuallyconcentric, located at an axial plane, and located radially outward fromthe planetary gearsets 28, 46, 48 such that they do not add to the axiallength of the gearbox. Similarly, clutches 96, 100 and brake 104 aremutually concentric and located radially outward from the planetarygearing 28, 46, 48. Clutches 76, 80, 96, 100 and brakes 88, 104, 106comprise the control elements.

As FIGS. 2A, 2B illustrate, the front cylinder assembly 36 is supportedfor rotation on the fixed front support 24 and carrier 34. The frontcylinder assembly 36 is formed with clutch actuation fluid passages,each passage communicating with one of the cylinders 114, 116 formed inthe front cylinder assembly 36. Cylinder 114 contains piston 78;cylinder 116 contains piston 82. One of the fluid passages in frontcylinder assembly 36 is represented in FIG. 2 by interconnected passagelengths 109, 110, 111, 112, through which cylinder 116 communicates witha source of clutch control hydraulic pressure. Another of the fluidpassages in front cylinder assembly 36, which is similar to passagelengths 109, 110, 111, 112 but spaced angularly about axis 11 frompassage lengths 109, 110, 111, 112, communicates a source of clutchcontrol hydraulic pressure to cylinder 114. Passage lengths 109 aremachined in the surface at the inside diameter of the front cylinderassembly 36.

The front cylinder assembly 36 is also formed with a balance volumesupply passage, similar to, but spaced angularly about axis 11 frompassage lengths 109, 110, 111, 112. The balance volume supply passagecommunicates with balance volumes 120, 122. As shown in FIG. 2A, thebalance volume supply passage includes an axial passage length 124,which communicates with a source of balance volume supply fluid andpressure, and a radial passage length 126, through which fluid flowsinto the balance volumes 120, 122 from passage 124. Passage 124 may be asingle drilled hole extending along a longitudinal axis and locatedbetween the two clutch balance areas of the A clutch and B clutch.Passage 124 carries fluid to cross drilled holes 126, which communicatewith the balance volumes 120, 122.

Coiled compression springs 128, 130, each located in a respectivebalance dam 120, 122, urge the respective piston 78, 82 to the positionshown in FIG. 2. Ring gear 34 is secured to front cylinder assembly 36by a spline connection 132.

Middle cylinder assembly 86 includes carrier 32, which is grounded onthe front support 24. Carrier 32 includes first and second plates 134,135 and pinion shafts secured to the plates, one pinion shaft supportingpinions 38, and the other pinion shaft supporting pinions 40. Plate 135is formed with a cylinder 140 containing a brake piston 90.

A source of brake actuating hydraulic pressure communicates withcylinder 140 through a series on interconnected passage lengths 142, 143and a horizontal passage length that extends axially from passage 143,through a web of carrier 32, between the sets of planet pinions 38, 40,to cylinder 140. These brake feed passages are formed in carrier 32.When actuating pressure is applied to cylinder 140, piston 90 forces theplates of brake 88 into mutual frictional contact, thereby holding sungears 54, 62 and shell 66 against rotation. A Belleville spring 146returns piston 90 to the position shown in FIG. 2, when actuatingpressure is vented from cylinder 140.

The front support 24 is formed with passages, preferably spaced mutuallyabout axis 11. These passages in front support 24 are represented in theFIGS. 1 and 2 by passage lengths 150, 151, 152, through which hydraulicfluid is supplied to clutch servo cylinders 114, 116, brake servocylinder 140, and balance dams 120, 122. A passage of each of the frontsupport passages communicates hydraulic fluid and pressure to cylinders114, 116 and balance dams 120, 122 of the front cylinder assembly 36through the fluid passages 109, 110, 111, 112, 113, 124 formed in thefront cylinder assembly 36. Another passage of each of the front supportpassages communicates hydraulic fluid and pressure to cylinder 140 ofthe middle cylinder assembly 86 through the fluid passages 142, 143 incarrier 32.

The front support 24 includes a bearing support shoulder 154, whichextends axially and over an axial extension 156 of the front cylinderassembly 36. A bushing 158 and bearing 160 provide for rotation of thefront cylinder assembly 36 relative to the front support 24. Thisarrangement of the front support 24, its bearing support shoulder 154,and front cylinder assembly 36, however, prevents radial access requiredto machine a passage or passages that would connect first passage 152 infront support 24 to the second passage 109 in the front cylinderassembly 36.

To overcome this problem and provide hydraulic continuity betweenpassage lengths 109, 152, first passage 152 is formed with an openingthat extends along a length of first passage 152, parallel to axis 11,and through an outer wall of the front support 24. The opening facesradially outward toward second passage 109. Similarly, second passage109 is formed with a second opening that extends along a length ofsecond passage 109, parallel to axis 11, and through an inner wall ofthe front cylinder assembly 36. The second opening faces radially inwardtoward first passage 152.

A first sleeve 162 is inserted axially with a press fit over a surfaceat an outer diameter of the front support 24, thereby covering theopening at the outer surface of passage length 152. Sleeve 162 is formedwith radial passages 164, 165, which extend through the thickness of thesleeve 162. Seals 176, located at each side of the passages 164, 165prevent leakage of fluid from the passages.

A second sleeve 170 is inserted axially with a press fit over the secondopening at the inside diameter of the front cylinder assembly 36,thereby covering and enclosing the length of the second opening in thesecond passage 109. Sleeve 170 is formed with radial openings, two ofwhich are represented in FIG. 2 by openings 172, 174, aligned with theradial passages 164, 165 formed in the first sleeve 162.

Sleeves 164 and 170 provides hydraulic continuity from the source offluid pressure carried in the passages of the front support 24 to thebalance dams 120, 122 and the servo cylinders 114, 116, 140, throughwhich clutches 76, 80 and brake 88 are actuated.

Sleeves 162, 170 also provide access that enables machining of the firstand second passages 152, 109 in the surface at the outside diameter offront support 24 and in the surface at the inside diameter of the frontcylinder assembly 36. FIG. 3 shows sleeves 162, 170 and three seals 176,which are fitted in recesses on sleeve 162 between each of its radialpassages 164, 165.

As FIG. 4 shows output pinion 70 meshes with a transfer gear 180, whichis formed integrally with transfer pinion 182 on a transfer wheel 184. Atransfer shaft 186, is secured at one end by a pinned connection 188 toa non-rotating housing component 190, and at the opposite end is seatedin a recess 192 formed in a non-rotating torque converter housingcomponent 194. Ball bearing 198 supports transfer wheel 184 on thetorque converter housing 194. Housing components 190, 194 comprise areaction component and may be formed integrally or preferably asseparate components.

Ball bearing 198 is supported radially by being seated on a surface 196of the torque converter housing 194. A shoulder 199 on torque converterhousing 194 contacts the right-hand axial surface of the inner race ofbearing 198, the second surface of bearing 198. A snap ring 200 contactsthe right-hand axial third surface 201 of the outer race of bearing 198.Shoulder 199 and snap ring 200 limit rightward axial movement of bearing198.

A shoulder 202 formed on gear wheel 184 contacts the left-hand axialfirst surface of the outer race of bearing 198. A thrust washer 204contacts a left-hand axial fourth surface 205 of the inner race ofbearing 198. The thrust washer 204 contacts a shoulder 206 formed ontransfer shaft 186. Shoulders 202 and 206 limit leftward axial movementof bearing 198

The ring gear 210 of a differential mechanism 212 meshes with transferpinion 182 and is supported for rotation by bearings 214, 216 on housing190, 194. Rotating power transmitted to output pinion 70 is transmittedthrough transfer gears 180, 182 and ring gear 210 to the input ofdifferential, which drives a set of vehicle wheels aligned with axis220.

A roller bearing 222 supports transfer wheel 184 on transfer shaft 186.The thickness of a washer 224, fitted in a recess 226 of housing 190, isselected to ensure contact between thrust washer 204 and the inner raceof bearing 198.

The output pinion 70 and transfer gears 180, 182 have helical gearteeth, which produce thrust force components in the axial directionparallel to axis 220 and in the radial direction, normal to the plane ofFIG. 4. A thrust force in the right-hand direction transmitted to thetransfer gear wheel 184 is reacted by the torque converter housing 194due to its contact at shoulder 199 with bearing 198. A thrust force inthe left-hand direction transmitted to the transfer gear wheel 184 isreacted by the housing 190 due to contact between snap ring 200 andbearing 198, contact between bearing 198 and thrust washer 204, contactbetween the thrust washer and transfer shaft 186, and contact betweenshaft 186, washer 224 and housing 190.

As shown in FIG. 1A, the D brake 104 includes a first set of thin discs230 secured to the outer race 232 of one-way brake 106 by a splineconnection, which permits the discs 230 to move axially and preventsthem from rotating relative to the race 232, which is fixed to thetransmission case or end cover against rotation.

Similarly, the D brake 104 includes a second set of thin discs 234secured to the inner race 107 of one-way brake 106 by a splineconnection, which permits the discs 234 to move axially and preventsthem from rotating relative to the inner race 107. Inner race 107 isfixed to the carrier 68 of gearset 46, such that they rotate together asa unit at the same speed. Preferably the outer and inner races 232, 107of one-way brake 106 are formed of a ferrous alloy of sintered powderedmetal, and discs 230, 234 are of steel. Preferably the one-way brake 106is a rocker one-way brake of the type having a pivoting rockers, eachrocker retained is a pocket and actuated by centrifugal force and acompression spring, as described in U.S. Pat. Nos. 7,448,481 and7,451,862.

The reaction spline for the D clutch 104 is preferably not formed in thealuminum case or end cover because of high local stresses caused by thethin discs 232, 234 used to reduce parasitic loss. The D clutch reactionsplines are formed as an integral part of the raceways of the one-waybrake 106. The brake 106 is then splined to the transmission case.

The final drive mechanism of FIG. 5 produces a drive connection betweenthe output pinion 70 and the input of the differential mechanism 212.Output pinion 70 meshes with output gear 270, which is supported on aball bearing 272 and roller bearings 274, 275. Bearing 272 is supportedon the transmission case 26; bearings 274, 275 are supported on anextension 276, which is bolted to the case.

A planetary final drive gearset 278 includes a sun gear 280, secured tothe output gear 270; a ring gear 282, secured to the input ofdifferential 212; a carrier 285, fixed against rotation by a splineconnection 284 to the cover extension 276; and planet pinions 287supported on the carrier 285 and meshing with the sun gear 280 and ringgear 282. The final drive gearset 278 drives the differential input at aspeed that is reduced relative to the speed of output gear 270 andreverses the direction of rotation relative to the direction of rotationof output gear 270. The differential drives the axle shafts, which aresecured to the driven wheels.

In accordance with the provisions of the patent statutes, the preferredembodiment has been described. However, it should be noted that thealternate embodiments can be practiced otherwise than as specificallyillustrated and described.

The invention claimed is:
 1. A final drive mechanism, comprising: apinion; a gear meshing with the pinion; a differential mechanism; anepicyclic gearset including an input driveably connected to the gear,and an output driveably connected to the differential, rotating slowerthan a speed of the gear, and rotating in a direction opposite thedirection of the gear.
 2. The drive mechanism of claim 1, wherein theepicyclic gearset further comprises: a sun gear secured to the gear; aring gear secured to the differential; a carrier fixed against rotation;and planet pinions supported on the carrier and meshing with the sungear and the ring gear.
 3. The drive mechanism of claim 2, wherein thesun gear is supported for rotation on roller bearings contacting atransmission case.
 4. The drive mechanism of claim 2, wherein the sungear is secured to the gear by a spline connection.
 5. The drivemechanism of claim 1, wherein the gear is supported for rotation on abearing contacting a transmission case.
 6. The drive mechanism of claim1, wherein the pinion is secured to a member of a second gearset thatchanges a speed of the pinion relative to a speed of a transmissioninput.
 7. A final drive mechanism, comprising: a first gearset producingspeed ratios at an output; a pinion; a shell connecting the output tothe pinion; a gear meshing with the pinion; a differential mechanism; asecond gearset including an input driveably connected to the gear, and asecond output driveably connected to the differential, rotating slowerthan a speed of the gear, and rotating in a direction opposite thedirection of the gear.
 8. The drive mechanism of claim 7, wherein thesecond gearset further comprises: a sun gear secured to the gear; a ringgear secured to the differential; a carrier fixed against rotation; andplanet pinions supported on the carrier and meshing with the sun gearand the ring gear.
 9. The drive mechanism of claim 8, wherein the sungear is supported for rotation on roller bearings contacting atransmission case.
 10. The drive mechanism of claim 8, wherein the sungear is secured to the gear by a spline connection.
 11. The drivemechanism of claim 7, wherein the gear is supported for rotation on abearing contacting a transmission case.
 12. A final drive mechanism,comprising: a first epicyclic gearset producing speed ratios at anoutput; a pinion driveably connected to the output; a gear meshing withthe pinion; a differential mechanism; a second epicyclic gearsetincluding an input driveably connected to the gear, and a second outputdriveably connected to the differential, rotating slower than a speed ofthe gear, and rotating in a direction opposite the direction of thegear.
 13. The drive mechanism of claim 12, wherein the second epicyclicgearset further comprises: a sun gear secured to the gear; a ring gearsecured to the differential; a carrier fixed against rotation; andplanet pinions supported on the carrier and meshing with the sun gearand the ring gear.
 14. The drive mechanism of claim 13, wherein the sungear is supported for rotation on roller bearings contacting atransmission case.
 15. The drive mechanism of claim 13, wherein the sungear is secured to the gear by a spline connection.
 16. The drivemechanism of claim 12, wherein the gear is supported for rotation on abearing contacting a transmission case.